Tejas Navaratna

Tejas completed a bachelor of science degree in chemical-biological engineering and physics at MIT in 2014 and is working towards a PhD in chemical engineering at the University of Michigan. At MIT, he enjoyed applying physics and engineering to biology through research and classes and plans to continue this in the future. Outside of academics, he enjoys outdoor recreation, especially climbing and hiking.

In about four or five billion years, our Sun will utter its final sigh as it runs out of material to fuse together. For stars much larger than our Sun, the end fate is rather different. They will first grow to become red giants, and then, when they run out of fuel, will undergo one of the most cataclysmic events in the universe. In less than a second, one of these giant stars collapses into a tiny city-sized object, and explodes outward, releasing more energy than our Sun has released in its entire lifetime! But amid all that light and heat, over 95% of a supernova's energy escapes in a massive outpouring of invisible neutrinos. Upwards of 10⁵⁸ neutrinos escape! This is much, much greater than the number of grains of sand in all the oceans on the Earth and the number of stars in the universe (and also, the product of these two numbers).

A supernova's light outshines the total light from the millions of other stars in its own galaxy. The most recent supernova visible to the naked eye occurred over 150,000 light years away. The most distant visible star of similar brightness is 100 times closer. A supernova that occurred 7,500 light years away in the year 1006 was brighter than a crescent moon and easily visible during the day. In fact, a supernova occurring closer than about 30 light years, more than five times farther than the nearest star, would kill most life on the Earth. Fortunately for us, there are no stars in our immediate neighborhood that pose a supernova threat.

In the 20th century, with the advent of better telescopes, astronomers linked various nebulae—clouds of gas, dust, and plasma—to supernovas that had occurred centuries ago. Not only could scientists find these supernovas, they could also determine what they were made of. To do this, they used an instrument called a spectrometer that determines the element composition of a light source. For example, a spectrometer can tell us if a star is burning hydrogen. Today, astrophysicists are armed with much more powerful telescopes and instruments that produce troves of data, but it is still not enough to understand the complete picture. For that, they need to collect data from the very early stages of a supernova's short-lived life.

In past decades, telescopes have been used to scour the sky, meticulously comparing current images with previous images, to detect new objects that could be supernovae. While this process is now automated at several large telescopes, it's still slow and error-prone and consumes valuable telescope time. Only after a supernova is found by such searching can fancier instruments, like x-ray, gamma ray, and other detectors be turned towards the supernova to take further measurements.

Searching the whole sky for a potentially very dim "new" star actually introduces a lag time in observation, which is a problem. The time it takes to confirm a supernova amongst false positive results and turn all other important instruments toward it means that scientists can't gather critical information from the very beginning of an event. That missing information could be very important for understanding the physics of supernovas, such as the role of neutrinos in fueling them.

Fortunately, those very neutrinos could be the key to catching early-stage supernovas. When the core of a very large star collapses, within a few seconds, a huge burst of neutrinos is generated. These extremely light particles do not interact with much at all. They pass right through the rest of the star, heading for the Earth (and the rest of the universe). Light from within the supernova may only emerge from the star hours later after it bounces around the whole star, getting absorbed and re-emitted like a high energy game of billiards. As a result, a supernova's neutrinos reach Earth before the supernova's light! Being able to detect these neutrinos would be a valuable "heads up" for astrophysicists, who could then point their instruments at the supernova before missing all the action.

One of the most famous supernovae was SN1987A—it's been the only supernova that astrophysicists got a good, close view of with modern instruments. It was a golden opportunity for observation, but it could have been better: the astrophysicists could have used a heads up! When the supernova's explosive light was first spotted from Earth in 1987, a mad rush to observe the supernova ensued. Interestingly, three neutrino detectors around the world did notice a burst of neutrinos a couple hours before the supernova became visible, but at the time, there was no early warning system in place and the telescopes were not ready when the explosion did become visible.

Today, the two communities want to bridge that communication gap, lest another golden opportunity slips by them. They created SNEWS, or the SuperNova Early Warning System. There are several neutrino detectors all over the world that are part of the SNEWS project. Kate Scholberg, a professor of physics at Duke University and SNEWS coordinator, writes that "if we have two experiments recording a signal at the same time, we can be pretty sure that it's not an accident." Supernova neutrinos have particular signatures, so the synchronization of all these detectors ensures that the possibility of a false alarm is minimal. Once the two separate detectors observe large events within a very short span of time, an email alert is sent out to astronomers all over the world.

Having access to the earliest light from a supernova could unravel a good deal of mystery surrounding supernovae. One of the major unknowns in supernova physics is whether or not so-called "failed" supernovas exist. These are events in which a large star collapses inwards but halts and does not explode. Some models have predicted that these do occur and form black holes, while others do not support the idea that such events could actually take place. Furthermore, the effect of neighboring objects, like companion stars, is not well understood. The light associated with a supernova's interactions with a nearby object would be most detectable early on.

You can sign up for SNEWS yourself and be one of the first to hear! According to Professor Scholberg, a supernova occurs in our galaxy about every 30 years, so we should see another one soon. And thanks to SNEWS, when that happens, all of us will, in unison, point our telescopes in the right direction!